JavaScript - Hover effect

var _elementID;
var _xOffset = 15;
var _yOffset = 15;
 
function GetMouseX( event )
{
    if ( !event )
    {
        event = window.event;
    }
      
    if ( event.pageX )
    {
        return event.pageX;
    }
    else if ( event.clientX )
    {
        return event.clientX + ( document.documentElement.scrollLeft ?  document.documentElement.scrollLeft : document.body.scrollLeft );
    }
    else
    {
        return 0;
    }
}
 
function GetMouseY( event ) 
{
    if ( !event ) 
    {
        event = window.event;
    }
      
    if ( event.pageY )
    {
        return event.pageY; 
    }
    else if ( event.clientY )
    {
        return event.clientY + ( document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop );
    }
    else
    {
        return 0;
    }
}
 
function Follow( event )
{
    if ( document.getElementById )
    {                  
        var element = document.getElementById( _elementID );
        
        if ( element != null )
        {
            var style = element.style; 
            style.left = ( parseInt( GetMouseX( event ) ) + _xOffset ) + 'px';
            style.top = ( parseInt( GetMouseY( event ) ) + _yOffset ) + 'px'; 
            style.visibility = 'visible';
        }
    }
}
 
function Show( elementID )
{
    if ( document.getElementById )
    {     
        _elementID = elementID;
            
        document.onmousemove = Follow;
    }
}
 
function Hide( elementID )
{
    if ( document.getElementById )
    {     
        _elementID = elementID;
            
        var divStyle = document.getElementById( _elementID ).style;
        divStyle.visibility = 'hidden';
      
        document.onmousemove = '';
    }
}

Example:

Test

<div id="Hover" style="background-color: White; color: Black; padding: 5px; position: absolute; visibility: hidden;">Test</div>
<div onmouseover="javascript:Show( 'Hover' )" onmouseout="javascript:Hide( 'Hover' )" style="background-color: Red; height: 100px; width: 100px;"></div>